Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Super-cooling

Sub-cooling or under-cooling

Normal cooling

2. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

3. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

4. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

5. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Carnot

Reversed Rankine

Rankine

6. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant entropy

Takes place at constant temperature

Takes place at constant pressure

7. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

8. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

9. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

10. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

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11. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

Capillary tubes

12. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Axial

Piston type reciprocating

13. The boiling point of ammonia is

-10.5°C

-77.7°C

-33.3°C

-30°C

14. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

15. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

16. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

17. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

18. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

19. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

20. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

Page 3 of 4

21. The capillary tube, as an expansion device, is used in

Water coolers

Room air conditioners

All of these

Domestic refrigerators

22. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

23. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Low

Any value

24. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.376

0.4

0.6

25. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-75.2°C

-135.8°C

26. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Zero

None of these

Negative

27. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Ericson

Stirling

Carnot

28. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Condenser, absorber and separator (rectifier)

Absorber

Evaporator

29. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Good electrical conductor

High risibility with oil

Low boiling point

30. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Any one of the above

Always less than unity

Equal to unity

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31. Most thermostatic expansion valves are set for a superheat of

10°C

20°C

15°C

5°C

32. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

15 bar

2 bar

8 bar

33. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

34. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

35. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

4.33

2.33

3.33

36. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

37. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Ammonia

Freon

Carbon dioxide

38. Rating of a domestic refrigerator is of the order of

10 tons

5 tons

0.1 ton

40 tons

39. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

40. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

9: 1

1: 3

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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